Major objective of the research program supported by this grant is to work out all of the detailed mechanisms involved in both moving and initiating DNA replication forks. The T4 bacteriophage replication apparatus is being used as the model system for these studies. To date, ten different T4 proteins have been purified to essential homogeneity. Both in vivo and in vitro studies demonstrate that each of these proteins is essential for T4 DNA replication. We plan to characterize the chemistry and function of each of these proteins in detail, including the eventual determination of their structure by x-ray crystallography.